Improved polyurethane elastomers

ABSTRACT

1. POLYURETHANE ELASTOMERS PREPARED BY A PROCESS COMPRISING REACTING AN ARGANIC POLYISCYANATE WITH AN ORGANIC COMPOUND HAVING ACTIVE HYDROGEN ATOMS WHICH ARE REACTIVE WITH -NCO GROUPS AND A CHAIN-EXTENDING COMPOSITION COMPRISING A MIXTURE OF A COMPOUND OF THE FORMULA   HO-CH2-CH2-O-(1,4-PHENYLENE)-C(-R)2-(1,4-PHENYLENE)-O-CH2-   CH2-OH   WHEREIN R IS HYDROGEN OR METHYL; WITH A COMPOUND SELECTED FROM THE GROUP CONSISTING OF C3 TO C7 ALKANE DIOLS OR A COMPOUND OF THE FORMULA   HO-CH2-CH2-NH-CO-(C(-R&#39;&#39;)(-R&#34;))X-(CO)Y-NH-CH2-CH2-OH   WHEREIN R&#39;&#39; AND R&#34; ARE THE SAME OR DIFFERENT AND REPRESENTS HYDROGEN OR C1 TO C4 ALKYL; X IS 0 TO 4 AND Y IS 0 OR 1 WITH THE PROVISO THAT WHEN Y IS 0, X IS 0 AND WHEN Y IS 1, X IS O TO 4

United States Patent US. Cl. 260-75 NQ Claims ABSTRACT OF THE DISCLOSURE Elastomeric polyurethane polymers are prepared by reacting a polyisocyanate with an organic compound having active hydrogen atoms which are reactive with NCO groups and a chain-extending composition comprising a mixture of a compound of the formula wherein R is hydrogen or methyl, with a compound selected from the group consisting of C to C, alkane diols or compounds of the formula wherein R and R" are the same or different and represent hydrogen or C to C alkyl and x is 0 to 4 and y is 0 or 1 with the proviso that when y is 0, x is O and when FIELD OF THE INVENTION This invention is a continuation-in-part of application Ser. No. 221,778, filed Jan. 28, 1972, and application Ser. No. 222,990, filed Feb. 2, 1972, both of which are now abandoned, and relates to polyurethane polymers and to a method of preparing the same. More particularly, this invention relates to elastomeric polyurethane polymers of improved physical and mechanical properties and to a method of preparing the same.

DISCUSSION OF THE PRIOR ART The production of cross-linked synthetic resins based on polyhydroxyl compounds, polyisocyanates and chain lengthening agents or cross-linking agents having reactive hydrogen atoms such as glycol, diamines, amino-alcohols and the like has been heretofore known. The proportions may be so chosen that free NCO groups remain and Patented Oct. 29, 1974 "Ice with cross-linking agents in a manner similar to crude rubher by the usual methods of the rubber industry, for example, on rollers. However, the elastomers obtained in many cases have only relatively low tensile strengths at elongations of from about 300% to about 500%. Fillers have heretofore been used to increase the modulus some- What, but do not improve the ultimate tensile strength. Moreover, tensile strengths are dependent to a considerable extent upon temperature, that is, they decrease rapidly with increasing temperature.

OBJECTS It is, therefore, an object of this invention to provide polyurethane polymers and a method of preparing the same which are devoid of the aforesaid problems and disadvantages. Another object of this invention is to provide improved polyurethane polymers. An additional object of this invention is to provide a method of preparing improved polyurethane polymers. A further object of this invention is to provide polyurethane polymers having a desirable combination of properties and to a process of preparing the same. A still further object of this invention is to provide a method for the preparation of polyurethane polymers having a wide range of desirable mechanical and physical properties. Yet another object of this invention is to provide elastomeric, nonporous polyurethane polymers having a high modulus and tensile strength with good elongation properties and lower permanent set and a method for preparing said polymers. It is a still further additional object of this invention to provide improved polyurethane polymers of good physical and mechanical properties and having a good appearance without the need for fillers.

SUMMARY OF THE INVENTION The foregoing objects and others which will become apparent from the following description are accomplished in accordance with this invention, generally speaking, by pro viding polyurethane polymers prepared by reacting a substantially linear compound having active hydrogen atoms as determined by the Zerewitinoif test, which active hydrogens are reactive with isocyanato groups, and an excess of an organic polyisocyanate with a chain extending composition comprising a mixture of a compound of the formula (I) R rrwcrn-cm-oQ- ({J-Q-O-CHr-ClIr-OH wherein R is hydrogen or methyl with a compound selected from the group consisting of C to C alkane diols or a compound of the formula (II) 0 O Hosannamilitiamen wherein R and R" are the same or different and represent hydrogen or C to 0, alkyl; x is 0 to 4 and y is 0 or 1 with the proviso that when y is 0, x is 0 and when y is 1,.xis0to 4;

in an amount at least sufiicient to react with essentially all the -NCO groups of the reaction product obtained from the organic compound having active hydrogen atoms and the organic isocyanate. Some representative compounds of the foregoing general formula (II) preferred for use according to the invention are, for example, N,N-bis(2-hydroxyethyl)urea, N,N'-bis(2-hydroxyethyl) oxalamide, N,N'-'bis(2-hydroxyethyl) Ina-.1

DETAILED DISCLOSURE OF THE INVENTION It is indeed unexpected that the advantages of this invention were to be obtained with the mixture of chainextending agents of this invention since the mixtures of chain-extending agents permits the preparation of polyurethane polymers having greatly improved appearance and having properties more desirable than the properties of the elastomers obtained with the use of the individual chain-extending agents alone. It was not to be expected that elastomeric polyurethanes of improved properties and appearance could be prepared utilizing mixtures of chain-extending agents without undesirably affecting the other properties of the elastomers.

Any suitable substantially linear organic compound containing active hydrogen atoms may be used in the process of this invention, such as, for example, dihydroxyl polyesters, polyalkylene ether glycols, dihydric polythioethers, dihydric polyacetals, polyester amides and the like but it is preferred to use a polyhydric poly alkylene ether, a polyhydric polythioether and most preferably a hydroxyl polyester obtained by a process which comprises condensing a polycarboxylic acid and a polyhydric alcohol or by condensing a caprolactone such as e-caprolactone to a polycaprolactone.

Any suitable hydroxyl polyester may be used in the process of this invention such as, for example, the condensation product of a polycarboxylic acid and a polyhydric alcohol.

Any suitable polycarboxylic acid may be used in the preparation of the hydroxyl polyester such as, for example, adipic acid, succinic acid, sebacic acid, suberic acid, oxalic acid, malonic acid, methyl adipic acid, glutaric acid, pimelic acid, azelaic acid, phthalic acid, terephthalic acid, isophthalic acid, thiodipropionic acid, maleic acid, fumaric acid, citraconic acid, itaconic acid and the like. Any suitable polyhydric alcohol may be used in the reaction with the polycarboxylic acid to form a polyester such as, for example, ethylene glycol, propylene glycol, butylene glycol, neopentyl glycol, amylene glycol, hexanediol, bis-(hydroxymethyl)cyclohexane and the like. Of course, the hydroxyl polyester may contain urethane groups, urea groups, amide groups, chalkogen groups and the like. Thus, the hydroxyl terminated polyester includes, in addition to hydroxyl terminated polyesters, also hydroxyl terminated polyester amides, polyester urethanes, polyetheresters and the like. Any suitable polyester amide may be used such as, for example, the reaction product of a diamine or an amino alcohol with any of the compositions set forth for preparing polyesters. Any suitable amine may be used such as, for example, ethylene diamine, propylene diamine, tolylene diamine and the like. Any suitable amino alcohol such as, for example, b-hydroxy ethylamine and the like may be used. Any suitable polyester urethane may be used such as, for example, the reaction of any of the above mentioned polyesters or polyester amides with a deficiency of an organic polyisocyanate to produce a compound having terminal hydroxyl groups. Any of the polyisocyanates set forth hereintfter may be used to prepare such compounds. 7 v

Any suitable polyetherester may be used as the organic compound containing terminal hydroxyl groups such as, for example, the reaction product of an ether glycol and a polycarboxylic acid such as those mentioned above, with relation to the preparation of polyesters. .Any suitable ether glycol may be used such as, for example, diethylene glycol, triethylene glycol, 1,4-phenylene-bis (hydroxy ethyl ether), 2,2-diphenyl propane-4,4-bis (hydroxy ethyl ether) and the like.

Any suitable polyhydric polyalkylene ether may be used such as, for example, the condensation product of an alkylene oxide with a small amount of a compound containing active hydrogen containing groups such as, for example, water, ethylene glycol, propylene glycol, butylene glycol, amylene glycol and the like. Any suitable alkylene oxide condensate may also be used such as, for example, the condensates of ethylene oxide, propylene oxide, butylene oxide, amylene oxide, styrene oxide and the like, and mixtures thereof. The polyalkylene ethers prepared from tetrahydrofuran may be used. The polyhydric polyalkylene ethers may be prepared by any known process such as, for example, the process described by Wurtz in 1859 and in the Encyclopedia of Chemical Technology, volume 7, pages 257-262, published by Interscience Publishers in 1951 or in U.S. Pat. No. 1,922,459.

Any suitable polyhydric polythioether may be used such as, for example, the reaction product of one of the aforementioned alkylene oxides used in the preparation of the polyhydric polyalkylene ether with a polyhydric thioether such as, for example, thiodiglycol, 3,3'-dihydroxypropyl sulfide, 4,4-dihydroxybutyl sulfide, 1,4-(b-hydroxy ethyl) phenylene dithioether and the like.

Any suitable polyacetal may be used such as, for example, the reaction product of an aldehyde with a polyhydric alcohol. Any suitable aldehyde may be used such as, for example, formaldehyde, paraldehyde, butyraldehyde and the like. Any of the polyhydric alcohols mentioned above with relation to the preparation of hydroxyl polyesters may be used.

Mixtures of any of the compounds of the classes set forth hereinabove may be used also.

The organic compound containing active hydrogen atoms should preferably be substantially linear or only slightly branched and have a molecular weight of at least about 600 and for best results, a molecular weight of from about 1000 to about 3000, a hydroxyl number of from about 75 to about 35 and an acid number less than about 2.

Any suitable organic diisocyanate may be used in reaction with the organic compound containing active hydrogen atoms to produce polyurethane polymers such as, for example, aliphatic, cycloaliphatic, aromatic and heterocyclic isocyanates, such as, alkylene, cycloalkylene and arylene diisocyanates which may be substituted with substituents unreactive with active hydrogen and isocyanato groups such as, for example, ethylene diisocyanate, ethylidene diisocyanate, propylene diisocyanate, butylene diisocyanate, hexamethylene diisocyanate, cyclopentylene-1,3- diisocyanate, cyclohexylene-1,4-diisocyanate, cyclohexylene-1,2-diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocynate and their isomeric mixtures, dimeric tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,2- diphenylpropane-4,4'-diisoeyanate, p-phenylene diisocyanate, m-phenylene diisocyanate, xylylene diisocyanate, 1,4- naphthylene diisocyanate, 1,5-naphthylene diisocyanate, diphenyl-4,4'-diisocyanate, azobenzene-4,4-diisocyanate, diphenylsulphone-4,4'-diisocyanate, dichlorohexamethylene diisocyanate, furfurylidene diisocyanate, l-chlorobenzene-2,4-diisocyanate and the like. Other suitable polyisocyanates are among those mentioned, for example,'in U.S. Pat. No. 3,382,215. It is preferred that aromatic diisocyanates be used for best results, 4,4'-diphenylmethane diisocyanate.

As set forth hereinabove, the preferred chain-extending mixtures of this invention comprise mixtures of bis(bhydroxyethoxyphenyl) methane or bis(b-hydroxyethoxyphenyl) propane with one of the compounds selected from the group of C to C alkane diols, preferably, 1,4- butane diol or N,N'-bis(2-hydroxyethyl) urea, N,N'-bis (Z-hydroxyethyl) oxalamide, N,N'-bis(2-hydroxyethyl) malonamide, N,N-bis(2-hydroxyethyl) succinamide and N,N-bis(Z-hydroxyethyl)adipamide. The components of the chain-extending mixture may be employed in any suitable proportions. However, it is preferred that the chainextending mixture comprise from about 10% to 95% bis(b-hydroxyethoxyphenyl) methane or propane, most preferably from about 50% to 90% bis(b-hydroxyethoxyphenyl) methane or propane, with the remainder being one or the other compounds.

In some cases it may be necessary to increase the rate of reaction of the active hydrogen containing organic compounds and the organic polyisocyanate and if this is desired, one may use any suitable catalyst for the isocyanate-active hydrogen reaction, such as, for example, tertiary amines, such as N-ethylmorpholine, dimethyl benzyl amine, dimethyl stearyl amine, N,N-endoethylene piperazine, triethylene diamine and the like as well as metal catalysts such as dibutyl tin dilaurate, dibutyl tin-di-Z- ethyl hexoate, stannous octoate, stannous oleate, lead naphthanate and the like and mixtures thereof.

The purpose of this invention is applicable to the preparation of elastomeric products by the various methods known to those skilled in the art. Thus, the organic compound containing active hydrogen atoms, the polyisocyanate and the chain-extending composition can be mixed together in the proper proportions and cast in the usual casting technique into a mold having the desired configuration. Also, this same result can be accomplished by first reacting the polyisocyanate and the organic compound containing active hydrogen atoms to obtain an --NCO terminated prepolymer and then mixing this prepolymer with the chain-extending composition in the casting technique.

In any case the reaction mixture is cast into a mold where it is cured at any suitable temperature and preferably at a temperature within the range of about 100 C. to about 150 C., the curing time being somewhat dependent on the temperature at which curing is effected. Most preferably, the final mixture of reaction components is cast into a mold and cured at a temperature of about 110 C. for about 24 hours.

The process is also useful in the millable gum technique wherein the organic compound containing active hydrogen atoms, the chain-extending composition and a deficiency of the polyisocyanate are first reacted to form a millable gum and then this millable gum is further mixed with an additional quantity of an organic polyisocyanate such as dimeric tolylene diisocyanate on a roll mill such as that used in the rubber industry, and the final product formed by a compression molding technique or the like. In this millable gum technique, a suitable peroxide such as, for example, dicumyl peroxide may be incorporated into the millable gum to bring about the cross-linking.

In addition, the process of this invention is useful in what has been termed the thermoplastic technique wherein the reaction compounds are mixed and caused to partially react. The reaction is then interrupted while the material can still be worked by thermoplastic techniques. At this point the material is generally in the solid state. This solid partially reacted material can be fabricated into the desired final form by molding techniques such as, for example, compression molding, injection molding, extrusion, and the like. In this technique, as well as in the casting and millable gum procedures, a one-shot mixing system or a prepolymer procedure can be followed.

The individual reaction components and the proportion in which they are added can be chosen according to the basic properties desired of the end product. However, it is preferred that the isocyanate be present in an amount sufficient to react with all of the active hydrogen atoms present and particularly in an amount such that a slight excess is present based on the active hydrogen atoms present in the other reaction components. For best results, it is preferred that the isocyanate be present in an amount such that the NCO to active hydrogen ratio is from about 1.0 to about 1.1.

UTILITY The polyurethane plastics obtained by the process of the present invention are useful in a variety of applications, such as, for example, the preparation of molded articles, tires, toys, shoe heels, bearings, gear wheels, valve seals, as insulated cable covering for electrical wire and the like.

EXAMPLES The invention is further illustrated but is not intended to be limited by the following examples in which all parts and percentages are by weight unless otherwise specified.

EXAMPLES 1-15 Elastomers were prepared in a mixer by employing polyester, chain-extender and isocyanate in a molar ratio of about 1:2:3.15 or l:3.38:4.6, respectively. The molar portion of a polyester having a molecular weight of about 2,000 and an OH number of about 58 prepared by condensing about 1 mol of adipic acid with about 1.09 mols of glycol is dehydrated by heating to a temperature of about 125 C. and reacted for about 30 to 50 minutes with the molar portion of 4,4'-diphenylmethane diisocyanate and the molar portion of the chain-extender mixtures set forth in the table below. The reaction mixture is pressed into a hot mold, removed and cured by heating to a temperature of about C. for about 16 hours. The resulting substantially homogeneous polyurethane plastics obtained exhibit the following physical characteristics as set forth in Table 1 in which the symbols employed have the following meanings:

I is bis(b-hydroxyethoxyphenyl)-2,2-propane II is N,N'-bis(2-hydroxyethyl) urea III is N,N'-bis(2-hydroxyethyl) oxalamide IV is N,N-bis(2-hydroxyethyl) malonamide V is N,N'-bis(2-hydroxyethyl) succinamide Formulation Ratio A is 1 molar part polyester 2 molar parts extender 3.15 molar parts isocyanate (5% excess) Formulation Ratio B is 1 molar part polyester 3.38 molar parts extender 4.6 molar parts isocyanate (5% excess) Elastomers prepared from bis(hydroxyethoxyphenyl)- 2,2-propane alone provide elastomers of unacceptable properties and unacceptable appearance. However, when the chain-extending compositions of this invention are employed, elastomers of acceptable properties as well as acceptable appearance are obtained. It was not to be expected that employing one of the compounds selected from N,N-bis(2-hydroxyethyl) urea, N,N-bis(2-hydroxyethyl) oxalamide, N,N-bis(2-hydroxyethyl) malonamide and N,N'-bis(2-hydroxyethyl) succinamide would exert a beneficial effect upon elastomers prepared utilizing bis(b-hydroxyethoxyphenyl) propane such that elastomers of improved appearance and acceptable properties would be produced.

TABLE 1 Molar percent Properties of I in chain I Formula- E1onga 300%, Shore Shore Chain extender tion, tion, Set, Tensile, modulus, hardness, hardness, Example number extender mixture ratio percent percent p.s.i. p.s.i. A D

100 A 425 500 500 71 28 100 B 360 5 7,500 5,700 97 58 90 A 475 0 5, 700 500 68 25 50 A 510 27 6, 525 1,400 83 32 50 A 600 45 5,700 800 72 38 90 B 375 2 3, 800 1, 400 91 46 50 B 350 40 6, 075 5, 100 92 43 50 B 400 30 7, 400 3, 850 83 42 50 B 350 7 5, 700 3, 700 93 52 90 A 450 0 5,250 400 68 25 50 B 375 30 5, 350 3, 500 91 49 0 A 495 108 5, 100 2, 550 89 45 0 A 600 55 6, 450 2, 400 82 35 0 A 415 96 4,800 2, 500 82 38 0 A 450 85 4, 650 2, 275 80 30 EXAMPLES 1627 Elastomers were prepared in a mixer by employing polyester, chain-extender and isocyanate in a molar ratio of about 1:2:3.15 or 1:338:46, respectively. The molar portion of a polyester having a molecular weight of about 2,000 and an OH number of about 58 prepared by condensing about 1 mol of adipic acid with about 1.09 mols of glycol is dehydrated by heating to a temperature of about 125 C. and reacted for about 30 to 50 minutes with the molar portion of 4,4'-diphenylmethane diisocyanate and the molar portion of the chain-extender mixtures set forth in the table below. The reaction mixture is pressed into a hot mold, removed and cured by heating to a temperature of about 110 C. for about 16 hours. The resulting substantially homogeneous polyurethane plastics obtained exhibit the following physical characteristics as set forth in Table 2 in which the symbols employed have the following meanings:

I is bis(b-hydroxyethoxyphenyl) methane II is 1, 4-butanediol III is N,N'-bis(2-hydroxyethyl) urea IV is N,N'-bis(2-hydroxyethyl) oxalamide V is N,N-bis(2-hydroxyethyl) malonamide Formulation Ratio A is 1 molar part polyester 2 molar parts extender 3.15 molar parts isocyanate (5% excess) Formulation Ratio B is 1 molar part polyester 3.38 molar parts extender 4.6 molar parts isocyanate (5% excess) While the use of bis(b-hydroxyethoxyphenyl) methane, 1,4-butanediol, N,N-bis(2-hydroxyethyl) urea, N,N'-bis (Z-hydroxyethyl) oxalamide and N,N-bis(2-hydroxyethyl) malonamide each alone as chain-extending agents produce elastomeric compositions of acceptable pr0perties for numerous applications it was not to be expected that using mixtures of the bis(b-hydroxyethoxyphenyl) methane compond with the other compounds as chain-extending compositions would permit the production of elastomeric compositions whose properties are more desirable and better than either component used singularly. For example, the use of a mixture of bis(hydroxyethoxyphenyl) methane and 1,4-butanediol produces an elastomer having a tensile strength of 7100 psi, greater than the tensile strength of elastomers produced from either bis(hydroxyethoxyphenyl) methane (6275 p.s.i.) or 1,4-butanediol (5700 p.s.i.) alone. Likewise, the tensile strengths of elastomers produced from mixtures of his (hydroxyethoxyphenyl) methane with N,N-bis(2-hydroxyethyl) oxal'amide (6850 and 7225 p.s.i.) is greater than the tensile strengths of elastomers from either compound used alone (6275 and 5100 p.s.i.). Similarly an elastomer produced from a mixture of bis (hydroxyethoxyphenyl) methane and N,N'-bis(2-hyd roxyethyl) urea has a tensile strength (8200 p.s.i.) greater than the tensile strength of elastomers produced from either compound alone (6450 and 6275 p.s.i.). In each instance the use of the chain-extending compositions of the invention produces elastomers of unexpectedly improved tensile strength without an undesirable effect on the other properties of the elastomers. In a similar manner the use of a chain-extending composition comprising a mixture of bis(hydroxyethoxyphenyl) methane with N,N-bis (2- hydroxyethyl) malonamide unexpectedly improves the modulus and set of the elastomer without undesirable effect on the other properties of the elastomer.

It is, of course, to be understood that any of the organic compounds containing active hydrogen atoms and any suitable organic polyisocyanate may be used in the working examples for the specific compositions utilized therein and that the above examples are merely illustrative of the invention.

It is to be understood that any of the components and conditions mentioned as suitable herein can be substituted for its counterpart in the foregoing examples and that although the invention has been described in considerable detail in the foregoing, such detail is solely for the purpose of illustration. Variations can be made in the invention by those skilled in the art without departing from the spirit and scope of the invention.

TABLE 2 Molar percent Properties of I in chain Formula- Elonga- 300%, Shore Shore Chain extender tion, tion, Set, Tensile, modulus, hardness, hardness, Example number extender mixture ratio p rcent P r t D- p A D 100 'A 500 60 6, 275 2, 000 38 0 A 575 42 4, 400 1, 400 89 38 0 A 500 55 6, 450 2, 400 82 35 0 A 495 108 5,100 2,550 89 45 0 A 415 96 4, 800 2, 500 82 38 90 A 500 30 6, 850 2,050 83 32 50 A 485 37 7, 225 2, 600 82 35 50 A 425 25 8, 200 1, 500 73 30 90 A 500 25 7, 1, 850 78 33 100 B 400 75 4, 3, 000 91 49 50 B 335 47 725 5, 000 94 41 90 A 450 45 2,300 80 34 What is claimed is:

1. Polyurethane elastomers prepared by a process comprising reacting an organic polyisocyanate with an organic compound having active hydrogen atoms which are reactive with NCO groups and a chain-extending composition comprising a mixture of a compound of the formula wherein R is hydrogen or methyl; with a compound selected from the group consisting of C to C alkane diols or a compound of the formula wherein R and R" are the same or diflerent and represent hydrogen or C to C alkyl; x is to 4 and y is 0 or 1 with the proviso that when y is 0, x is 0 and when y is 1, x is 0 to 4.

2. The elastomer of claim 1 wherein the alkane diol is 1,4-butanediol.

3. The elastomer of claim 1 wherein the compounds represented by the formula (II) are selected from the group consisting of N,N-bis(2-hydroxyethyl) urea, N,N'- bis(2-hydroxyethyl) oxalamide, N,N'-bis(2-hydroxyethyl) malonamide, N,N'-bis(2-hydroxyethyl) succinamide and N,N-bis(2-hydroxyethyl) adipamide.

4. The elastomer of claim 1 wherein the compound of the formula (I) is bis(b-hydroxyethoxyphenyl) methane or bis(b-hydroxyethoxyphenyl) propane having a purity of at least 95 percent.

5. The elastomer of claim 1 wherein the active hydrogen containing compound is substantially linear or only slightly branched and has a molecular weight of from 10 about 1000 to about 3000, a hydroxyl number of from about to about 35 and an acid number less than about 2.

6. The elastomer of claim 1 wherein the chain-extending mixture comprises from about 10 percent to about percent by weight based on the weight of chain-extending mixture of bis (b-hydroxyethoxyphenyl) methane or his (bhydroxyethoxyphenyl) propane and the balance a compound selected from the group consisting of C to C alkane diols or the compounds of the formula (H).

7. The elastomer of claim 1 wherein the organic compound containing hydrogen atoms reactive with -NCO groups is selected from the group consisting of dihydroxyl polyesters, polyalkylene ether glycols, dihydric polythioethers and dihydric polyacetals.

8. The elastomer of claim 1 wherein the organic polyisocyanate is an aromatic diisocyanate.

9. The elastomer of claim 8 wherein the aromatic diisocyanate is 4,4'-diphenylmethane diisocyanate.

10. The elastomer of claim 1 wherein the organic p0lyisocyanate is reacted with the organic compound containing active hydrogen atoms reactive with -NCO groups in a first step to prepare an --NCO terminated prepolymer and reacting said -NCO terminated prepolymer with the chain-extending composition.

References Cited UNITED STATES PATENTS 3,357,954 12/1967 Kirkaldy 260-75 3,226,344 12/1965 Schwartz et al. 26075 3,388,100 6/1968 Thoma et a1 260-75 NA 3,711,440 1/1973 Chadwick 260-775 AM MELVYN I. MARQUIS, Primary Examiner US. Cl. X.R.

26067 TN, 75 NP, 77.5 AM 

1. POLYURETHANE ELASTOMERS PREPARED BY A PROCESS COMPRISING REACTING AN ARGANIC POLYISCYANATE WITH AN ORGANIC COMPOUND HAVING ACTIVE HYDROGEN ATOMS WHICH ARE REACTIVE WITH -NCO GROUPS AND A CHAIN-EXTENDING COMPOSITION COMPRISING A MIXTURE OF A COMPOUND OF THE FORMULA 